The potential biological effects of in utero radiation exposure of a developing fetus include prenatal death, intrauterine growth restriction, small head size, mental retardation, organ malformation, and childhood cancer. The risk of each effect depends on the gestational age at the time of exposure, fetal cellular repair mechanisms, and the absorbed radiation dose level. A comparison between the dose levels associated with each of these risks and the estimated fetal doses from typical radiologic examinations lends support to the conclusion that fetal risks are minimal and, therefore, that radiologic and nuclear medicine examinations that may provide significant diagnostic information should not be withheld from pregnant women. The latter position is advocated by the International Commission on Radiological Protection, National Council on Radiation Protection, American College of Radiology, and American College of Obstetrics and Gynecology. However, although the risks are small, it is important to ensure that radiation doses are kept as low as reasonably achievable.

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Dissociation of ozone in the Chappuis bands has been used as an O atom source to study isotope effects occurring in the O(3P)+O2(3∑g) recombination reaction. The ozone produced was found to be enriched in both of its heavy isotopes. The pressure dependence (5–1000 torr) and temperature dependence (127–360 K) of this isotope effect have been investigated. The enrichment is approximately constant from 5 torr to 100 torr and decreases at higher pressures. It increases with temperature, with 50O3 showing a slightly faster rate of increase than 49O3. The results of this experiment have clearly isolated the source of the isotope effect to the gas phase O(3P) + O2(3∑g) recombination reaction. For comparison, we also present isotope ratios of ozone formed in an electric discharge. None of the results, however, have shown the large enhancement of 40% or more in mass 50 observed in some stratospheric measurements.

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